don't apply invalid ordering when preloading hmt associations.

closes #8663.

When preloading a hmt association there two possible scenarios:

1.) preload with 2 queries: first hm association, then hmt with id IN ()
2.) preload with join: hmt association is loaded with a join on the hm association

The bug was happening in scenario 1.) with a normal order clause on the hmt association.
The ordering was also applied when loading the hm association, which resulted in the error.

This patch only applies the ordering the the hm-relation if we are performing a join (2).
Otherwise the order will only appear in the second query (1).

1 files changed, 6 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 8317e4e2f5..5521a1579a 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,11 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Preloading ordered `has_many :through` associations does no longer
+    apply invalid ordering to the `:through` association.
+    Fixes #8663.
+
+    *Yves Senn*
+
 *   The auto explain feature has been removed. This feature was
     activated by configuring `config.active_record.auto_explain_threshold_in_seconds`.
     The configuration option was deprecated and has no more effect.